The present invention relates in general to the detection and isolation of interconnect faults in an automotive wiring system, and more specifically to the application of pulse signals to a dedicated test line included in the wiring harness and the monitoring of reflections of the pulse signals from impedances in the test line to determine the existence and/or location of improperly connected connectors.
The electrical interconnect system of an automobile takes the form of a wiring harness which is normally partitioned into segments. Each segment includes a number of individual conductors. Individual segments are joined by electrical connectors at either end. Furthermore, an individual conductor or conductors may leave the main bundle of wires in a particular segment to form a subsegment which extends to another connector. The shape of the wiring system is irregular and cannot normally be classified as a star, ring or other regular configuration.
Because of the segmented structure of a wiring harness, point-to-point connections between the electrical system load devices interconnected in the wiring system normally include many connectors and conductor segments. These connectors include expansion connectors, termination connectors, and junction blocks. An expansion connector interconnects the partitioned segments of the wiring harness, i.e., expands the wiring harness. Termination connectors interconnect the electrical devices of the vehicle with the wiring harness system, i.e., at terminations of the wiring harness segments. Thus, the electrical devices are referred to as termination devices. A junction block is a device for cross-connecting wiring harness segments, electrical system devices, individual wiring harness conductor wires, and other junction blocks. The conductors and connectors of the wiring harness system can be either electrical, optical, or both.
Improperly connected or nonconnected connectors result in the partial or complete failure of an electrical device or devices connected to the electrical system. Failure of a critical electrical system component may cause the vehicle to quit (i.e., lose drivability) which often requires the vehicle to be towed in for service. Interconnect problems that may inadvertently be present include both complete failures to properly interconnect connectors and partial interconnect failures such as when connectors are not fully inserted to their snap-lock position. These interconnect problems may not become apparent until extended use of the electrical system causes damage to an improperly connected device or until vibrations cause a partially connected connector to separate.
In order to maximize vehicle reliability and to minimize warranty and repair costs, it is desirable to reduce interconnect faults by detecting and isolating their occurrence. A simple and inexpensive system is needed which is adaptable to testing after final assembly, testing during service, and monitoring and fault prediction during vehicle use. Prior art wiring harness testing apparatus are complex and are not readily adaptable to testing under all circumstances.
U.S. Pat. No. 4,689,551, issued to Ryan et al, discloses a wiring harness testing apparatus which tests for proper assembly of the wiring harness itself, i.e., before the prefabricated harness is installed into a vehicle and before the termination connectors of the harness are connected to the vehicle electrical components. The termination connectors of the harness must be plugged into the testing apparatus or to a special adaptor for testing. Each wire in the harness being tested is connected at one end to a current source and at the other end to ground by switches in the testing apparatus that are connected to each wire. Since the testing apparatus must be connected to the termination connectors of the wiring harness, the tests are not possible after the wiring harness is connected into the vehicle electrical system.
European patent application 164570, in the name of Goto et al, discloses a wiring harness checker wherein a checker connects to each termination connector of the wiring harness being tested. The checker is connected to the harness on a test table and checks the conduction of individual conductors in the harness in both or either direction. Thus, the checker is useful only for testing before final assembly since there is no ability to check the harness after it is connected to the electrical components in the vehicle.
U.S. Pat. No. 4,271,388, issued to Schaling, discloses another testing apparatus requiring direct connection of the tester to the conductors and connectors of the cable set being tested. Shift registers are connected to one end of each conductor or connector to be tested. Light emitting diodes and logic circuits connected to the other end of each conductor or connector monitors signals received from the shift registers and indicate the correct or incorrect assembly of the wiring harness itself. Thus, the tester is suitable for testing only before final assembly with the electrical system components of the vehicle.
U.S. Pat. No. 3,718,859, issued to Arlow, discloses a test element in the form of a connector insert which allows monitoring of individual conductors while a wiring harness is interconnected and in operation. The test element plugs into and interconnects the pins of a pair of connectors. The test element includes terminals on its outer surface, each terminal being electrically connected to one of the connector pins and thus to one of the individual conductors of the wiring harness. The terminals may be contacted by a meter to monitor a signal on the corresponding individual conductor. Therefore, the individual conductor can only be tested when the corresponding electrical device is energized. Furthermore, the failure to monitor an expected signal from a conductor does not reveal the location or reason for the occurrence of the fault.
These are some of the deficiencies which the present invention overcomes.
Copending application Ser. No. 07/504,502 teaches a modified automobile electrical system including a dedicated test line in at least a portion of the electrical system. The dedicated test line includes additional conductors in the wiring harness and dedicated and modified connector components. By examining terminal characteristics of the dedicated test line after final assembly of the electrical system, faults in the interconnection of harness expansion connectors and termination connectors are detected and their location isolated. Thus, the dedicated test line includes one or more test points for examining the electrical characteristics of the test line. The dedicated test line includes a termination conductor within a termination connector, such that the termination conductor is included in the dedicated test line only when the device connected by the termination connector is properly interconnected with the electrical system.
Thus, the invention of the copending application achieves fault detection and isolation by connecting test equipment to two or more test points in the dedicated test line. In order to simplify the testing operation, it would be desirable to detect and isolate faults while requiring only one connection to the dedicated test line.